Cultures of dissociated postganglionic sympathetic neurons will be prepared as previously described by this laboratory. Three aspects of synaptic function will be investigated: 1. The neurons form cholinergic synapses with each other. Most synaptic endings of cell bodies have been found to contain small dense cored vesicles characteristic of adrenergic endings. Attempts will be made to inject physiological identified cholinergic neurons with electron-opaque markers so that a direct test can be made of the question whether cells that secrete acetylcholine also contain dense cored synaptic vesicles. 2. The ability of the neurons to form effective junctions with smooth muscles from several sources will be tested. 3. Further tests will be made of the pharmacology of the cultured neurons to see if they possess receptors characteristic of adult sympathetic neurons in vivo. Bibliographic references: Nurse, C.A. and P.H. O'Lague (1975) Formation of cholinergic synapses between dissociated sympathetic neurons and skeletal myotubes of the rat in cell culture. Proc. Nat. Acad. Sci. 72, 1955-1959. O'Lague, P.H., P.R. MacLeish, C.A. Nurse, P. Claude, E.J. Furshpan and D.D. Potter (1976). Physiological and morphological studies on developing sympathetic neurons in dissociated cell culture. Cold Spring Harbor Symposia, Vol. 40, in press.